GPUs do not wear down from being ran at 100%, unless they're pushed past their voltage limits, or gravely overheating.

You can buy a GPU that's been used to mine bitcoin for 5 years with zero downtime, and as long as it's been properly taken care of (or better, undervolted), that GPU functions the exact same as a 5 year old GPU in your PC. Probably even better.

GPUs are rated to do 100%, all the time. That's the point. Otherwise it'd be 115%.

Yeah that's not how it works in practice in a datacenter with the latest GPUs, they are basically perishable goods.

You don't run your gaming PC 24/7.